The invention relates to bistable shape memory effect, SME, actuators, and more particularly to improvements for retaining the actuator at the end of its travel stroke.
SME alloys are known in the art and exhibit a given mechanical movement in response to heating above a transition temperature. The movement is definite, predictable and repeatable. A one-way SME element can be externally biased to return to its original position upon cooling below the transition temperature. A two-way SME element returns without external bias.
Bistable SME actuators are known in the art. A pair of opposing SME elements are connected to an actuator movable along a travel stroke between first and second positions. The first SME element may be heated by directing electric current flow therethrough to heat the SME element above its transition temperature to move the actuator to its first position. After cooling of the first SME element, the actuator may be moved to its second position by heating the second SME element, e.g. by directing electric current flow therethrough.
Hopkins et al U.S. Pat. No. 3,725,835 shows a bistable SME mechanism having an actuator 37-39, and first and second SME elements 29 and 33 coupled to the actuator and moving the actuator between respective first and second positions upon current flow through the respective SME elements causing heating thereof above the transition temperature.
Hochstein U.S. Pat. No. 4,544,988 shows a bistable SME mechanism with magnetic retaining means at the end of the travel stroke of the actuator.
The present invention provides various retainers for retaining the actuator at the end of its travel stroke, including upon cooling of a one-way SME element which may otherwise cause slight return repose movement of the SME element.